1. Field of the Invention
This invention relates to a sensor device and particularly to a sensor device which can detect a rotational angular velocity, inclination and linear acceleration and is utilized for automobile body control, correction of video camera shake, and so on.
2. Description of the Related Art
FIG. 8 is a block diagram showing the circuit of a sensor device employed for automobile body control, and so on. The sensor device 10 contains a vibrator 12. The vibrator 12 contains a vibrating body 14 of a rectangular solid as shown in FIG. 9. The vibrating body 14 is formed by joining, for example, two piezoelectric substrates 16 and 18. These piezoelectric substrates 16 and 18 are polarized so that their polarization is opposite to each other as shown by the arrows in FIG. 9. On one piezoelectric substrate 16, a groove 20 is formed so as to extend in the length direction of the vibrating body 12 in the middle of the width direction. Further, two grooves 22 and two grooves 24 extending in the width direction of the piezoelectric substrate 16 are formed so as to sandwich the portions corresponding with the two nodal points at bending vibration of the vibrating body 14.
On the surface of the piezoelectric substrate 16 divided by these grooves 20, 22, and 24, electrodes are formed. Among these electrodes, the electrodes 26 and 28 formed between the inside grooves 22 and 24 are used as detection portions for outputting signals in response to a vibration of the vibrating body 14. Further, on the other piezoelectric substrate 18, a common electrode is formed.
The vibrator 12 is supported by supporting members 32, 34, 36, and 38 formed by metal wires, etc. The supporting member 32 is connected to the electrodes 40 sandwiched by the two grooves 22 by welding, soldering, etc. This supporting member 32 is electrically connected to the electrode 26. Similarly, the supporting member 34 is connected to the electrode 42 sandwiched by the two grooves 24. This supporting member 34 is electrically connected to the electrode 28. Further, the supporting members 36 and 38 are connected to the common electrode 30 at the portions corresponding to the nodal points of the vibrating body 14. These supporting members 32, 34, 36, and 38 are formed in a bent shape and contained in a case 44.
The electrodes 26 and 28 of the vibrator 12 are connected to buffers 50 and 52, respectively. These buffers 50 and 52 are connected to a synthetic circuit 54, and the sum of the output signals from the buffers 50 and 52 is obtained in the synthetic circuit 54. The output signal of the synthetic circuit 54 is returned to an oscillation circuit 56, and amplified and phase shifted in the oscillation circuit 56. In this way, an excitation signal is produced, and the excitation signal obtained is input into the common electrode 30. Further, the buffers 50 and 52 are connected to a differential circuit 58, and the difference between the output signals from the buffers 50 and 52 is obtained. The output signal of the differential circuit 58 is input into a synchronous detection circuit 60, and detected in synchronization with the signal of the synthetic circuit 54. The signal detected in the synchronous detection circuit 60 is integrated in a integration circuit 62 and amplified in a DC amplifier.
In this sensor device 10, the vibrating body 14 vibrates under bending mode in the direction normal to the surface on which the common electrode 30 is formed, by an excitation signal obtained in the oscillation circuit 56. At this time, because the supporting members 32, 34, 36, and 38 support the portions corresponding to the nodal points of the vibrating body 14, there is little vibration leak of the supporting members 32 through 38. However, it cannot be said that there is no vibration leak from the supporting members 32 through 38, and the supporting members 32 through 38 are slightly vibrated. At this time, because the supporting members 32 through 38 are formed in a bent shape, the vibration of the supporting members 32 through 38 is absorbed, which prevents the vibration from leaking to the case 44.
Further, from the differential circuit 58, the difference between the signals output from the electrodes 26 and 28 is output. The output signal of the differential circuit 58 is detected in synchronization with the signal of the synthetic circuit 54 at the synchronous detection circuit 54. In the absence of any rotation, because the bending condition of the electrode portions 26 and 28 of the vibrating body 14 is the same, the same signal is output from the electrodes 26 and 28 as shown in FIG. 10. Therefore, any signal is not output from the differential circuit 58.
In such a condition, when rotation takes place about the axis of the vibrating body 14, a Coriolis force acts and the vibration direction of the vibrating body 14 is changed. Because of that, the bending condition of the electrode portions 26 and 28 is made different, and a difference is caused between the signals output from the electrodes 26 and 28. For example, as shown in FIG. 11, when the output signal of the electrode 26 increases, the output signal of the electrode 28 decreases. Therefore, from the differential circuit 58, the difference between these signals is output. Furthermore, because the change of the vibration direction of the vibrating body 14 is in accordance with the strength of the Coriolis force, the output signals of the electrodes 26 and 28 are also changed to be proportional to the Coriolis force. Further, because the output signal of the synthetic circuit 54 is the sum of the signals of the electrodes 26 and 28, the output signal of the differential circuit 58 and the signal of the synthetic circuit 54 are in phase. Therefore, by detecting the output signal of the differential circuit 58 in synchronization with the signal of the synthetic circuit 54, only the positive portion of the output signal of the differential circuit 58 can be detected. And by integrating the output signal of the synchronous detection circuit 60 through the integration circuit 62 and by amplifying it using the DC amplifier 64, a positive DC signal proportional to the Coriolis force can be obtained.
When the vibrator 12 is rotated inversely, as shown in FIG. 12, the output signal of the electrode 26 decreases and the output signal of the electrode 28 increases. Therefore, the output signal of the differential circuit 58 becomes in opposite phase to that in FIG. 11. On the contrary, because the output signal of the synthetic circuit 54 is in phase with FIG. 11, only the negative portion of the output signal of the differential circuit 58 is detected at the synchronous detection circuit 60. Therefore, a negative DC signal proportional to the Coriolis force can be obtained at the DC amplifier 64. Thus, the magnitude of a rotational angular velocity can be detected from the output signal of the DC amplifier 64, and the direction of a rotational angular velocity can be detected from the polarity of the output signal of the DC amplifier 64.
The use of such a sensor device 10 as, for example, a rollover sensor of automobiles, etc. has been considered. When an automobile is turned sideways, the roll-over sensor is to detect the rotational angular velocity and inflate a side air bag, and as a result, protect people from a traffic accident, which might result in injury or death. Further, the detection of rotational angular velocity using a sensor device is used for preventing video camera shake.
However, when an automobile is turned sideways while it is parked in a sloping place, the time from the start to finish of the turning is shorter than the case where the automobile is parked in a horizontal place, and accordingly it is required to inflate a side air bag by detecting only a little rotational angular velocity. That is, on the basis of the initial inclination of an automobile the timing of inflation of a side air bag must be controlled. Further, when the side of an automobile is bumped by another, a signal concerning the rotational angular velocity of the automobile turning sideways may be erased by acceleration noise due to the bump, and the processing of the signal is made difficult. In order to detect all these three conditions, an angular velocity sensor, an inclination sensor, and an acceleration sensor are needed.
Further, the correction of video camera shake by detection of the rotational angular velocity has become common, but a horizontal detection is considered for an image stabilization system as a next step. This relates to a rotational movement and after all the detection of absolute horizontality is required.
The present invention can solve the aforementioned drawback associated with the conventional art and provides a sensor device which is able to detect not only rotational angular velocity, but also inclination and linear acceleration.
The sensor device for detecting a rotational angular velocity, an inclination and a linear acceleration, comprises a vibrating body, two detection portions to output signals in response to a vibration of the vibrating body, a differential circuit to output the difference between the signals from the two detection portions, a first synchronous detection circuit and second synchronous detection circuit to detect the output signal of the differential circuit in synchronization with the signal from a synthetic circuit. In the first synchronous detection circuit and second synchronous detection circuit, the output signal from the differential circuit is detected in synchronization with respective signals having a phase difference of 90xc2x0.
In such a sensor device, a weight can be added to the vibrating body.
Further, supporting members for supporting the vibrating body are contained and a weight may be added to these supporting members.
In the absence of any rotation, the output signals from the two detection portions are in phase and of the same level. Here, when a rotational angular velocity is applied to a vibrator, the vibration direction of the vibrating body is changed due to Coriolis force and the level of the output signals from the two detection portions alters, but they are in phase. When the output signals from the two detection portions are in phase, the difference between the signals becomes in phase with the output signals of the two detection portions.
When gravity and linear acceleration are applied in a direction different from the vibration direction of the vibrating body, different stresses are applied to the two detection portions, a difference between the resonance frequencies of the portions is caused, and phase-shifted signals are output from the detection portions. When the difference between such signals is output, a signal having a phase difference of about 90xc2x0 from the output signals of the detection portions at the time when gravity, etc. are not applied can be obtained. Because of that, between the output signal obtained from the differential circuit when a rotational angular velocity is applied and the output signal obtained from the differential circuit when gravity, etc. are applied, a phase difference of about 90xc2x0 is caused. Therefore, by detecting the output signal of the differential circuit in synchronization with a signal of a phase difference of 90xc2x0 rotational angular velocity can be detected and at the same time gravity or linear acceleration can be detected.
In such a sensor device, by addition of a weight to the vibrating body, or by addition of a weight to the supporting members for supporting the vibrating body the stress due to gravity and linear acceleration can be increased, and the detection sensitivity of these can be improved.
According to the invention, a sensor device for detecting all of rotational angular velocity, inclination, and linear acceleration can be obtained. Consequently, by using the sensor device the timing of inflation of an automobile air bag can be effectively controlled and video camera shake can be also effectively prevented.
For the purpose of illustrating the invention, there is shown in the drawings several forms which are presently preferred, it being understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown.
Other features and advantages of the present invention will become apparent from the following description of the invention which refers to the accompanying drawings.